We will expose 18 adult male baboons to chronic psychosocial stress, diet induced hyperlipidemia, and diet induced elevation in bold pressure in order to test the hypothesis that program of graded aerobic exercise results in decreased extent and severity of experimentally induced atherosclerosis. We will examine the combined effects of stress and graded aerobic exercise on atherosclerosis in an animal model, where environmental and nutritional variables are controlled while neuroendocrine, metabolic and psysiologic variables are measured by means of an instrumented tether system. This experiment is designed to provide initial answers for two interrelated questions: (1) does exersise ameliorate the adverse effects of stress, diet and aggressive behavior on atherosclerosis, and (2) what are the underlying physiologic, metabolic, neuroendocrine and behavioral mechanisms by which exercise modfiies the effects of psychosocial stress on atherosclerosis. The experiment uses: (1) resistance of stable social organization (dyadic coalitions) to the introduction of intruders, (2) perturbation of a stable social dominance hierarchy by intruders as a model of social stress; (3) graded work on a treadmill as a model of exercise; (4) baboons who will be fed on atherogenic diet; and (5) an instrumented tether system that allows us to obtain measurement of cardiovascular and biochemical variables in fully conscious baboons who are unrestrained within the confines of their cage. The three experimental treatment groups consist of sedentary (n=6), light exercise (n=6) and moderate exercise (n=6). We will measure cardiovascular function in terms of heart rate, systolic, diastolic and mean blood pressure using an indwelling catheter/transducer; circulating mediators of cardiovascular function (plasma renin, electrolytes and vasopressin); hormonal indicators of sympathetic system arousal and stress response (plasma catecholamines, cortisol, and testosterone); aggressive behavior (tension, threat, attack); physioloigcal indicators of exercise (blood lactate, muscle papillary density and enzyme activity) and lipids (serum cholesterol, HDL, LDL and VLDL cholesterol). The animals will be autopsied and the hypotheses tested with respect to the effects of exercise, physiologic, metabolic and behavioral variables on atherogenic lesion.